Solid feeding means fob fluid-type



y 6, 1952 c. TROST ETAL 2,596,088

SOLID FEEDING MEANS FOR FLUID-TYPE PULVERIZER Filed Feb. 9, 1949 lnventor 34 CONRAD TROST Fla. 3 J. WVILLIAM HOLDCRAF'T of the solid material.

Patented May 6, 1952 2,596,088 ICE SOLID FEEDING MEANS FOR FLUID-TYPE PULVERIZER Conrad Trost and Joseph William Holdcraft,

Moorestown, N. J assignors, by mesne assignments, to Freeport Sulphur Company, New York, N. Y., a corporation of Delaware Application February 9, 1949, Serial No. 75,424

2 Claims.

This invention relates in general to a reentrant circulatory pulverizer and more particularly to an improved method and means for feeding material into said pulverizer and grinding same whereby the operating efficiency and production capacity thereof are substantially increased.

It has been found as a result of both commercial practice and experimental tests that the production'capacity, the operating efiiciency and the range of use of presently known types of circulatory pulverizers or grinding mills, such as the one disclosed in the Andrews Patent Number 2,032,827, are limited by their means for feeding the material to be pulverized into the grinding chamber of the pulverizer. A commonly used material feeding means, hereinafter referred to as the injection feeding tube, is comprised of a tube which connects a hopper to said grinding chamber. A gas or fluid, which is forced under pressure through said tube, entrains partially pulverized material falling from said hopper into the tube and conveys it into said grinding chamber. The injection feeding tube, whose general operation is well known to the art raises several problems. Sometimes it becomes plugged with the material being fed through it, especially when such material has a waxy texture or when it is fed too rapidly. Since there is a constant pressure within said grinding chamber, such a stoppage in the feeding tube will cause the material being pulverized in the chamber to back up said tube. This is referred to as a blowback and is very detrimental to the operating efliciency of the machine. Unsuccessful attempts have been made to overcome feeding tube stoppages by enlarging the tube. However, beyond a certain point, enlargement interferes in other respects with the operation of the pulverizer.

The feeding tube fluid, which is preferably the same as the grinding fluid emitted from the side walls of the grinding chamber, necessarily enters the grinding chamber at an angle to the path of the grinding fluid therein and thereby creates a considerable turbulence. It was once thought that turbulence contributes to the comminution Experiments, however, in which the various factors contributing to pulverization were studied photographically, showed that turbulence caused practically no comminution, whereas its disadvantages effects, such as excessive wear, kickbacks and lost energy, definitely limit the productivity of the pulverizer.

As disclosed in said Andrews Patent No. 2,032,827, the maintenance of a uniform vortex of circulating fluid in the grinding chamber is necessary for eflicient pulverizing and classifying action upon the solid material. It has been found that material introduced by the injection feeding tube, or by other methods heretofore used, enters the vortex erratically and usually with instantaneous bursts due to alternate build-up-and release through the tube entrance to the grinding chamber. This causes distortion of the inwardly spiralling vortex and the resultant turbulence causes entrainment of oversized particles in the exhaust gases from said chamber. This effect is especially noticeable at higher rates of operation.

It becomes apparent therefore, that the injection feeding tube means of supplying solid material to the grinding chamber is unsatisfactory because it limits the productivity of the pulverizer by creating a wasteful turbulence and by frequent stoppages.

It has also been found that the feeding tube fluid, which constitutes between 15% and 30% of the fluid circling in the grinding chamber, is considerably decelerated during the entrainment and acceleration of the solid material conveyed thereby. Therefore, much energy is expended by the grinding fluid in accelerating the feeding tube fluid, which energy might otherwise be used to pulverize additional solid material. This energy loss exists in addition to the losses arising from the turbulence created in the grinding chamber and the resultant disturbance of the vortex pattern of the grinding fluid.

Therefore, a need becomes apparent for an improved means and method of introducing solid material, which may be partially comminuted, into the grinding chamber of a circulatory pulverizer without the encumbrance of the feeding tube fluid which materially reduces the efficiency and capacity of the puverizer.

The same above cited problems are encountered in all circulatory type pulverizers using the injection method of feeding the partially comminuted material, whether they are of the circular or oval, open center or tubular ring type, and the scope of this invention in its broadest aspects is intended to apply to all such pulverizers.

Accordingly, it is a primary object of this invention to provide an improved method and means for feeding solid material into the grinding chamber of a circulatory type of pulverizer or mill, whereby the production capacity and operating efliciency of the pulverizer may be substantially increased beyond the capacity and efliciency obtainable with presently known types of solid material feeding means and methods.

A further object of this invention is to provide an improved method and means, as aforesaid, whereby the range of use of a circulatory type pulverizer may be expanded to include materials, such as the waxy and amorphous types, which cannot now be effectively pulverized in mills equipped with presently known types of material feeding means.

A further object of this invention is to provide an improved method and means, as aforesaid, whereby the amount of pressurized fluid required to operate a given pulverizer at peak output may be substantially reduced without decreasing the yield of the pulverizer. v

A further object of this invention is to provide an improved method and means, as aforesaid, whereby the turbulence incident to the injection method offeeding the solid material into the grinding chamber is greatly reduced or substantially eliminated, thereby removing the excessive energy losses and wear of the grinding chamber walls which accompany such turbulence.

A further object of this invention is to..pro

vide an improved method and means, as afore said, which does not disturb the vortex action within the grinding chamber, which action effects a classification of the pulverized particles wherein the larger particles continue to circle nearthe outer perimeter of the chamber Whereasthe smaller. particles move toward the center and are drawn off by the exhausting fluid.

Other objects. and purposes of thisinvention will become apparent to persons familiar with this type of equipment upon referring to the accompanying drawings and upon reading the following specification.

Inorder to meet those objects and purposes heretofore mentioned, as well as others incidental thereto and associated therewith, we. have pro.- vided a mechanical feeding device which, in one preferred. embodiment, is comprised. of. a tube communicating between a materials hopper and the grinding chamber. from. the hopper to the grindin chamber. byv a screw which is rotatably supported snugly within said tube. The end of the screw adjacent to the grinding chamber is spaced sufficiently. away. from said chamber that the mouthof. the tube may be choked and thereby assure. that the material will. enter the grinding. chamber in. a solid mass. Normally, the mouth. of the tube is slightly. constricted to effect such choking. A.means isprovided for rotating the screw and thereby feeding a. continuous mass of. material. throughv the said tube mouth.

The leading portion of. thesolid mass of. materialiis preferably struck. by grinding fluid. emitted from a jet in the grinding. chamber peripheral wall and directed atv said. mass asv it protrudes through the mouth of thefeedingstube. Thus, the said. entering face-of said. massis eroded, or

The material. is. moved cates with the grinding chamber ll.

4 illustrated in the above mentioned Andrews patent. It has a cylindrical grinding chamber II which is surrounded, adjacent to its circumferential wall !2, by an annular header 3. The pulverizer H3 is provided with a pair of flat parallel plates i4 and I5 which intersect the axis of the pulverizer Iil'perpendicularly. The circumferential wall i2 is provided with a plurality of jet openings [.6 which communicate between the annular header l3 and the grinding chamber H, and which are preferably so positioned that the paths of the fluid emitted from said jets are substantially tangent to one or more circles about the axis of the grinding chamber i I in. a. manner well knownv and well establishedin the art.

An. oiftake. pipe ll, which is preferably coaxial with the cylindricalgrinding chamber H extends into said grinding chamber through a suitable opening in one of the plates, here the plate 14, of the pulverizer Ill. The grinding fluid andsufiiciently pulverized particles entrainedthereby escape through the offtake pipe l'iand are conveyed to. suitable. separatingmeans (not shown) in the. conventional manner. A suitable grinding fluid, suchas compressed. air or steam, is supplied. under pressure to the annular header i3 from an appropriate source (not shown) through the supplypipelB.

The mechanical.feedingdevice Z 2, to which this invention relates, includes a feeder tube 2.!- (Figure 1-) which. at. one end. extends through a. suitable opening in the plate 14 of the reentrant circulatory pulverizer l0 so that said tube communi- The said one end of the feeder tube 2! preferably doesnot extend beyond the inner surface 23 of. the. plate 14, and-is advantageously provided with an annular,.internal,ridge'24- which restricts the opening of the feeder tube 2| adjacent to the grinding chamber. The ridge may bev increased or de creasedin size, or in some cases may be eliminated entirely, according to the naturalcohesiveness of the material being ground. The less the abraded, both. by the rapidly moving grinding fluidfrom. said jet and by the particles of. material which have earlier been broken away from said. solid mass by said. jet and entrained in the circulating. grinding fluid. The solid mass may be fed into the chamber at a constant, controlled rate which creates little or no disturbance within the grinding chamber.

For. illustrations of the improved feeding device to which this invention. relates, attention is di'. rected to the accompanying drawings in which:

Figure 1 is a. brokenand partially sectioned side elevation view. of a conventional circulatory pulverizer providedwithout improved mechanical feeding device.

Figure 2 is a. fragmentary view of a portion of said pulverizer and a modified type of mechanical feeding device;

' Figure3 is a fragmentar View of. thestufiing boxand bearing indicated in. Figurel but-shown on anenlarged scale. a

CONSTRUCTION The embodiment'of my. invention illustrated in Figural of the accompanyingdrawings is shown, by wayof example, in cooperation with. a conventional reentrant circulatory pulverizer- H] of the general type, exceptin forthe feeding means,

natural cohesiveness the. larger the ridge must be. In any event, it should be of such size as to insure that the material is compacted before, it enters the grinding chamber.

However, since the feeder screw displaces a certain amount or the solid material throughout that portion of the feeder chamber in which said screw is positioned, the chamber mouth is preferably choked down by at least an amount corresponding to thedisplaced area of the screw thereby effecting an even and constant flow of solid material through the mouth 25.

It will'he clearly understood that'the exact size or shape of the mouth. 25 provided by the annular ridge 24 is not intended to impose. any limitations upon this invention, for these will vary according to the cohesiveness of. theparticular materials involved and the feed rates used providing only that the material is fedinto said chamber in a solid, compacted mass.

The exact point at which, and the angle with which, the feeder tube 2 l communicates with the grinding. chamber it may be varied from; that which. isshown in the illustrations. without. departing from the scope of. the invention..; The tube2l. may communicate with the. chamber H either through onev of the plates M or i5v or through the circumferential. wall I2 and. more than. one feeder tube, may be used with a single grinding chamber. Generally, however, it-seems preferable in most instances to have. the tube 2| communicate with. the chamber H through one of said plates l4 and l5 and be substantially perpendicular thereto at the circle of I maximum velocity of the grinding fluid. In the type of grinder illustrated by the above mentioned Andrews patent, this circle is approximately tangent to the path of the grinding fluid emitted from said jets. Further, it seems to be of some importance whereon said circle, especially with relation to the grinding jets, the tube mouth 25 is located, it being normally advantageous to have a grinding jet impinge substantially directly upon the plug as it protrudes from said mouth. Under some circumstances, such as where the material to be pulverized is either very cohesive or relatively hard, it is practically imperative that this direct impingement be provided.

A feeder screw 26 is rotatably and snugly housed within the tube 2| so that the inner end 21 thereof, adjacent to the pulverizer l0, approaches but does not extend through the mouth'25 into the grinding chamber Said inner end 21 of the screw 26 is preferably, but not necessarily, inclined to the axis of the said screw. The outer end 28 of said screw 26 is important that direct impingement by a jet be provided with a screw plate 30 which is secured to, or is integral with, a coaxial shaft 29 extending out of the end 3| of the feeder tube 2| remote from the pulverizer ID. Suitable means, such as an adjustable stufling box 32 of any conventional type may be supported upon the end 3| of the tube 2| and encircle the shaft 29 in a conventional manner to prevent the escape of grinding fluid through the end 3| of said feeding tube before material being fed therethrough isv formed into a solid mass.

In this embodiment of the invention, the stuffing box 32 (Figure 3) is comprised of a flanged cylindrical, housing 33 threadedly engaging the tube end 3|, a flanged gland 34, and suitable packing 35. The gland 34 is urged toward the housing 33 by conventional means, such as the bolt and nut arrangement 36, thereby compressing the packing 35 against the shaft 29 and effecting a seal therearound.

The shaft 29 may be rotatably supported upon a base 31 by any convenient, conventional bearings 38. A gear pinion 39 may be secured upon said shaft between said bearings 38 for rotation thereof by any suitable means (not shown).

The screw 26 and the shaft 29 may be adjusted axially toward or away from the pulverizer ID by any convenient means. One operable means of accomplishing this axial adjustment is comprised of a pair of spaced thrust collars 4| and 42 secured to that end of the shaft 29 remote from the screw 26, and a thrust head 43 surrounding said collar 4| and entering the space between the collars 4| and 42. An externally threaded adjustment screw 44, which is coaxial with said shaft 29 is secured to the thrust head 43 at one end thereof and to a crank 45 at the other end thereof. The screw 44 is threadedly engaged by and extends through an adjustment post 46 which is supported upon the base 31.

Accordingly, rotation of the adjustment screw 44 by the crank 45 in one direction causes said head 43 to bear against the collar 42 and thereby urge the shaft 29, hence the screw 26, toward the pulverizer l6. Rotation of the screw 44 in the opposite direction causes said head 43 to bear against the collar 45 and thereby draw the shaft 29, hence the screw 26, away from the pulverizer ID.

A materials hopper 41 communicates with the cylindrical feeder chamber 48 within the feeder tube 2| through a siutable opening therein intermediate the extremities thereof. The screw plate 3|.) inhibits the escape of the material into the stuffing box.

Material to be pulverized, which may be in a granulated, or other partially comminuted condition, is placed in the hopper 4'! and conveyed by the screw 26 through the chamber 43 into the grinding chamber MODIFICATIONS A modified mechanical feeding device 5|, illustrated in Figure 2, is comprised of a feeder tube 52 which is substantially identical to the feeder tube 2| (Figure 1). However, in this modification, the feeder screw 26 and the associated actuating mechanism are replaced by a plunger 53, which is actuated toward and away from the grinding chamber I la by any suitable and conventional means (not shown) such as a hydraulic pressure device. This type of mechanical feeding device is somewhat limited in its operation in that it cannot of itself affect a continuous feed of material into said grinding chamber but it avoids the expense and problems of screw feed operations. However, if two or more of said modified devices 5| are used in conjunction with the same pulverizer, a substantially continuous operation may be accomplished by operating them alternately. It will be recognized, therefore, that although the mechanical feeding device 22 and the modified device 5| are specific embodiments'of the invention which can accomplish the desired result, other modifications will be found to lie within the broadest scope contemplated by this in vention.

OPERATION The material to be pulverized, which may be partially preground or otherwise partially comminuted, is placed within the hopper 47, the

I feeder screw 26 is rotated until the material or feed is conveyed through the feeder chamber 43 to the mouth 25 of the feeder tube 2|. Where the material is not sufliciently cohesive to form the solid mass readily, the mouth 25 may be choked by means of the ridge 24 and the screw 26 may be initially run at a higher rate of speed than normal in order to start the formation of the mass, or the material may be initially treated with some cohering agent, such as water or oil, to assist in initially forming a solid mass. In any event, the screw will be started a few seconds before the grinding fluid is released into the grinding chamber to assure that the plug is well formed before the grinding chamber pressure is is imposed upon it. The pressure behind the grinding fluid, which flows through the supply pipe l8 into the annular header I3, is gradually increased as said fluid flows into the grinding chamber II where it soon circulates therein at a high rate of speed. As the material is fed by the screw 26 through the feeder tube 2| it is compacted into a solid mass and emerges through the mouth 25 in such form.

The further the screw 26 is from the chamber II, the greater the torque becomes upon said screw to force the material through the mouth 25. However, it has been found that the material in the tube 2| resists the back pressure of the grinding chamber more effectively when the screw 26 is rather substantially spaced from said grinding chamber in order to permit the formation of a sufiiciently long and solid plug at the mouth of the tube to block the escape of grinding 7. fluid; therethrough. moved back fromthe mouth while the speed and circulating load of the fluid and'material are being built up, during which time the static pressurewithin the chamber H is highest and the material in the tube is relatively, loosely packed and least resistant to back pressure; As the speed of the fluid and load increases and the static pressure in the grinding chamber decreases, the screw 26 is moved toward the chamber until at full operating speed the screw is as close to the mouth 25 as possible without permitting the escape of grinding fluid through said feed tube 2|.

The grinding fluid emitted from said impinging jet and/or circulating in the chamber ll strikes the mass of material as it protrudes through the mouth 25 breaking off particles of the materialin an abrading type of action. These particles are then further struck by the grinding jets and otherwise handled in the grinding chamber in the manner fully disclosed in the aforesaid. Andrews Patent No. 2,043,827. It will be clearly recognized that substantially the entire energy of the grinding fluid emitted through the jet opening 16 is absorbed in the abrasion of the solid mass emerging through the mouth 25, and in the acceleration, circulation, comminution and offtake of the particles abrading from said mass. None of the grinding fluid energy is dissipated in. turbulence caused by, or in the need for accelerating, any other material, such as the gas of the conventional injection type feeder.

The rate of feeding is controlled so'that the exposed surface of the solid mass is at all times nearly flush with the adjacent wall of the grinding chamber. Thus, the protrusion of the solid mass into the grinding chamber is at all times sufliciently small that the turbulence created thereby in the grinding stream is negligible. However, due to the higher efliciency of this method of feeding and grinding, the feed rate in any given case will actually be higher than for; conventional injection feeding under similar conditions. Furtherfore, the mechanical feeding device does not disturb or upset the vortex action which moves the sufficiently small particles of pulverized material toward the exhaust pipe I? and tends to hold the large particles near the radially outer portion of the grinding chamber where they may be exposed to further comminution, particularly by the cutting force of the grinding fluid emitted through the jets l6.

EXPERIMENTAL DATA.

The following examples are typical examples of the operation of a pulverizer equipped with an. improved mechanical feeding device to which this invention relates.

A fifteen inch diameter reentrant circulatory pulverizing mill of conventional type was fitted with a mechanical feeding device" having a screw feeder as shown in Figure 1. The screw was eighteen inches long and two inches in diameter, and had a screw pitch of 4'inches. The distance from the screw inner end 21 to the plate inner surface 23, which in this particular machine may be varied from 1% inches to 3% inches wasfirst held so that said screw inner end 21 was about as far away from said wall inner surface 23- as the. adjustable stuffing box 32 would permit for reasons hereinabove described. The hopper 41, which was positioned approximately ten inches from the plate 14, had a. 4-inch. opening in its- Therefore, the screw is square inch or more, while the grinding cham-- ber H was substantially empty. As the load of circulating fluid and. material in the pulverizing grinding chamber increased, the back pressure decreased to from two to four pounds per square inch. Therefore, it was found desirable to maintain a relatively large space between the end of thescrew 21 and the wall inner face 23 while thepulverizing machine was starting in order to place a larger amount of material, in the mouth 25' and thereby prevent a blow back during this period. As the speed and load of the-machine were increased, and the back pressure reduced accordingly, the feeder screw was'moved towardv the pulverizing; chamber, thereby reducing the amount of power required to urge the feed material through the mouth 25. V

The feedmaterial, consisting in this example of partially comminuted sulphur ranging in size from- A; inch in diameter to less than 50 mesh, was fed by the feeder screw 26 into the grinding chamber H at arate of 437 pounds per hour. The feeder screw 26 was rotated at 175 R. P. M. and required 0.2 amps. at 110 volts of alternating current. Air, under a pressure of 100 pounds per square inch, was supplied to the annular header I3; from whence it was emitted through the jet openings l6 at a rate 286 C. F. M. free air. The average particle size of the product carried off through the exhaust pipe I! was 3.2 microns, said product containing less than 0.01 per cent of particleslarger than 325 mesh.

Example II The data in thefollowing table was obtained in testsof the commercial type, 24 inch diameter reentrant circulatory pulverizer as disclosed in the Andrews Patent No. 2,032,827. The pulverizer was, first operated in a conventional manner with an injector feed mechanism such as shown in: the above mentioned patent. This injection feed. mechanism was then replaced with the mechanical feeding device 22 (Figure 1). The material with which. the pulverizing unit was charged consisted of a partially pulverized hard talc, 99.1 per cent of which could pass through a 3 25 mesh screen and had an average particle size of 1.8 microns. The following table indicates the relative capacities and efficiency of the two types of feeding mechanism, both of which were used under as nearly identical and optimum conditions as possible: i

TABLE I Mechan- Airlrcssurc (p. s. i.).. 100 .00 C. F. M. (Free Air). 1,080 Feed Rate (lbs; per lir.) 1. one 7 l 786 Average Size of Product (Microns) l. 1.40 C.,F. M. of air per lb. of feed per biz... 1.08 5 Lbs. handled per cubic ft. (Free air) 0. 0154;

It will be noted from Table I that the mechanithe pulverizer, which was operated at maximum output with both feeding mechanisms, by 78 per cent while decreasing the quantity of air required by 26 per cent. The pulverizer, when operated with the mechanical feeding device, demonstrated an overall increase in efficiency of about 140 per cent over the efficiency of the pulverizer equipped with the injection feed mechanism, while the average size of the product was decreased approximately per cent.

The following table represents the results of another test on a commercial mill of the type shown in said Andrews patent, operated at maximum output first with a conventional injection type feed mechanism and then with the screwtype mechanical feed device above described to pulverize precrushed tale of 100 mesh size:

It can be seen from the above table that the mechanical feed device increased the productive capacity of the mill by 125 per cent while the efficiency of the compressed air used was increased by more than 175 per cent.

It will be noted that a substantial saving, namely 200 C. F. M., in the amount of compressed air actually required is made when the improved type feeding unit is used. This is per cent of the air used with the injection system and means that about 1000 pounds of air per hour is eliminated from the grinding chamber. As much energy is required to accelerate this 1000 pounds of air to the very high velocities inside the grinding mill as is required to accelerate 1000 pounds of feed material. Therefore, it is believed that the increase of 1000 pounds per hour in the yield of pulverized material is substantially due to the elimination of the air used in the injection system, which in this particular case would amount to about-l000 pounds by weight.

Table III was recorded from a test of a commercial mill of the same size and type used for the above tables. It was operated at maximum output with both feeding mechanisms, in which a 50% DDT composition, having a particle size of The increase in capacity of the mill obtained with the mechanical feeding device in the foregoing test amounted to about 35% over the mill capacity with the injection feed device. The increase in fluid efficiency, that is the increase in pounds of material ground per cubic foot of air used, obtained with the mechanical feeding device amounted to about 80% over the mill capacity with the injection feed device.

Although the above mentioned drawings and description apply to one particular preferred embodiment of the invention, itis not my intention, implied or otherwise to eliminate other variations or modifications {of my improved mechanical feeding mechanism which will accomplish the desired result while remaining within the scope of the invention, unless specifically stated to the contrary in the hereinafter appended claims.

We claim:

1. In a device for compacting and feeding a mass of partially comminuted material into the grinding chamber of a fluid, circulatory pulverizer in which a grinding fluid is circulated, the combination comprising: a tube having a cylindrical feed chamber communicating at one end thereof with the grinding chamber, the adjacent end of said tube stopping short of said grinding chamber; a closure means disposed within the other end of said feed chamber and a hopper communicating with said feed chamber interme diate the ends thereof; a screw rotatably and axially reciprocably supported within said feed chamber and spaced from said grinding chamber; means, including a shaft extending through said closure and secured to said screw for effecting rotation and for axial adjustment thereof with respect to said grinding chamber; and an annular ridge extending internally from, the walls of said feed chamber adjacent to said one end thereof, the area defined by said ridge being equal to the cross-sectional area of said feed chamber less the area absorbed by said screw, whereby said mass of material will have a substantially constant density throughout said feed chamber and will present an unbroken front as it enters said grinding chamber.

2. In a mechanical device for compacting and feeding a homogeneous mass of partially comminuted material through an opening in the sidewall of the grinding chamber of a fluid, reentrant, circulatory pulverizer in which a grinding fluid is circulated, the combination comprising: a tube having a cylindrical feed chamber of constant diameter communicating at one end thereof with said grinding chamber through said opening, the adjacent end of said tube being flush with the inner surface of said sidewall; a closure means disposed within the other end of said feed chamber and a hopper communicating with said feed chamber intermediate the ends thereof; a screw rotatably, and axially adjustably, supported within said feed chamber, said screw being spaced from said grinding chamber; means, including a shaft secured to that end of said screw remote from said grinding chamber and extending through said closure, for rotating said screw and for effecting axial adjustment thereof with respect to said grinding chamber; and an annular ridge extending internally from the walls of said feed chamber adjacent to said one end thereof, the area defined by said ridge being equal to the cross-sectional area of said feed chamber less the area absorbed by said screw, whereby said mass of material will have a substantially constant density throughout said feed chamber and will present an unbroken front as it enters said grinding chamber.

CONRAD TROST. J. WILLIAM HOLDCRAFT.

(References on following page) 11 7 REFERENCES CITED Number The following references are of record in the ii] of thi 1: nt: II e S e 2,498,005

UNITED STATES PATENTS 5 Number Name Date w, 643,637 Ensberg Feb. 20, 1900 Number 1,675,941 Lindsay July 3; 1928 177 ,0 13- 2,032,827 Andrews 'Ma.y 3, 1936 Y 570g86'5 I Name- Date G'oss June 9; 1942 Man-n Dec. 25, 1 945 R'afton Feb'f21, 195'0 FO EIGN PATENTS" V 7 Country Date Germany 1 Oct. 23;. 1906 Great-Britain J'uly 26, 1945 

